William E. Kurtin

PHOTOCHEMISTRY OF THE MODEL PHOTOTROPIC SYSTEM INVOLVING FLAVINS AND INDOLES–I. FLUORESCENCE POLARIZATION AND MO CALCULATIONS OF THE DIRECTION OF THE ELECTRONIC TRANSITION MOMENTS IN FLAVINS*

Abstract— The fluorescence polarization spectra of riboflavin, lumiflavin, and alloxazine under different conditions have been obtained. It has been shown that the polarization spectrum of riboflavin is not affected significantly by media such as D2O‐glycerol (50: 50) and castor oil. Our data do not indicate the anomalous spectral shift of riboflavin in castor oil, in contrast to the previous finding described by Thomas. The electronic structures of lumiflavin and alloxazine are similar to that of riboflavin, as revealed by the fluorescence polarization measurements and the molecular orbital calculations. The Pariser‐Parr‐Pople semiempirical SCF ASMO CI computations have been performed to compare the calculated transition moments with the polarization data. The theory predicts an angle of 42° between the 450 and 365 nm transition oscillators, in reasonable agreement with the experimental angle of about 49°. It has been shown, from the comparison of the calculated and observed spectral quantities, that the pseudo‐heteroatom model for treating methyl groups in the flavin molecule is not adequate. The group orbital and inductive approximations appear to be satisfactory. Finally, the implication of the present findings has been briefly discussed in connection with phototropism.

THE NATURE OF THE LOWEST TRIPLET CONFIGURATION OF FLAVINS

Abstract— The phosphorescence spectrum of riboflavin has been reexamined at 77°K in an ethylene glycol: water matrix. The phosphorescence occurs at approximately the 605 nm (ca. 2‐·05 eV) region, in reasonable agreement with the theoretical calculations of 1·6–1·8 eV [21]. The emission was found to be negatively polarized, and to have a relatively long lifetime (0·56 sec). On the basis of this data and additional theoretical results, it is concluded that the lowest triplet of riboflavin is of 3(τ,τ*) type. Upon addition of potassium iodide, the phosphorescence emission is enhanced through spin‐orbit perturbation. The presence of oxygen (atmospheric pressure) in the frozen glass apparently has no effect on the emission. The phosphorescence spectra of alloxazine are also presented. Results of the present work have been applied to the photodephosphorylation of menadiol diphosphate in elucidating its mechan ism involving the riboflavin triplet and singlet oxygen.

Electronic structures and spectra of some natural products of theoretical interest—I: Molecular orbital studies of anthocyanidins

Abstract Anthocyanidins are naturally occurring plant pigments. The HMO, ω-SCF with ω = 0·5 and 1·4 and Pariser-Parr-Pople semiempirical SCF ASMO CI have been employed to study the electronic properties of these compounds. In general, the results from the different methods show at least semi-quantitative consistency with repect to predictions for spectra, charge densities, and geometry of the molecules. The colors of the anthocyanidin flower pigments are explained by the PPP method in excellent agreement with the experimental data. In addition, the theoretical π-dipole moments and the directions of the transition moments have been obtained by the PPP method.

THE CHARGE DISTRIBUTION IN THE EXCITED STATES OF SOME INDOLES

THE NEED for information on the electronic structures of the excited states of biomolecules has increased as a result of contemporary attempts to understand the photochemical properties of biomolecules, particularly flavins and aromatic amino acids. Considering the current theories and speculations on the mechanism of the quenching of the indole emission and the mechanism of phototropism, a knowledge of the electronic structures of ground and excited state indole molecules would be valuable in determining this mechanism. For example, two recent publications were concerned with the interpretation of the fluorescence properties of tryptophan derivatives in terms of the electron density of the excited states[l, 21. Since the calculated electron densities of indoles in the excited states are desirable for such interpretations, this note presents the electron density maps for indole, indole 3-acetic acid, and indole 5-carboxylic acid in their ground, lowest singlet, and lowest triplet states. The calculations were performed using the Pariser-Parr-Pople SCF MO method with limited configuration interaction [3,4], as outlined previously [ 5 , 6 ] . Figure 1 shows the electron density distribution for indole, while Fig. 2 depicts the charge distribution in indole 3-acetic acid. The methylene bridge in Fig. 2 was treated by the group orbital approximation[7]. It can be seen that the?r-electron density on the N decreases upon excitation to the lowest singlet (fluorescent) and triplet (phosphorescent) states. Changes in the electron density also occur at various positions of the ring carbons, as well as in the side chain. The most noteworthy result is the prediction that the side chain affects the charge redistribution pattern in the excited states of indole 3-acetic acid. Therefore, it is not safe to use the electron density map of indole for the interpretation of the fluorescent states of substituted indoles such as tryptophan. For example, position 4 shows an increase in the n--electron density of the fluorescent state of indole (Fig. I ) , while the opposite trend is seen in Fig. 2. However, qualitative use of the indole data for its derivatives can be made. In Fig. 2, the effect of the side chain on the electron density distribution in the excited states (particularly in the fluorescent state) is partly due to a slight intramolecular charge transfer (0-03 electron) via the hyperconjugation mechanism. The comparison of indole 5-carboxylic acid (Fig. 3) with indole (Fig. 1) also reveals the substitution effect, particularly at positions 2,4 and 7. In the case of indole 5-carboxylic acid, the substituent effect appears to be due to the partial charge transfer from the ring

Molecular luminescence studies of flavins. II. Interactions involving the excited states.

The effects of experimental geometry on the theoretical polarizations of the S1 ← S0 and S2 ← S0 bands of π→π* type in riboflavin have been examined. Polarizations of these two bands are characterized by an angle between them in the range of 20—28° and are relatively insensitive to the input geometry. Thus the predicted polarizations are generally in agreement with fluorescence polarization spectrum of riboflavin at 77°K. Alloxazine forms a strong complex with KI, and the fluorescence and phosphorescence from the charge transfer states have been characterized by means of luminescence and photoselection measurements. Riboflavin did not form a strong complex with KI, but it forms aggregates (dimer) more readily than alloxazine. The excited states of flavins can be populated by the weak dipole-dipole coupling mechanism of energy transfer from 1La states of indoles to the S2 state of flavins. The measured critical distances estimated from the fluorescence depolarization experiments range from 31 Å for indole to 40 A for indole-2-carboxylic acid in glycerol-methanol mixture (9:1) at 263°K.

Soluble dietary fiber protects against cholesterol gallstone formation

BACKGROUND Epidemiological studies have suggested that soluble dietary fibers are hypocholesterolemic and may inhibit cholelithiasis. METHODS Thirty prairie dogs were placed on a cholesterol-supplemented lithogenic diet. Ten animals received 5% psyllium (PSY) and 10 animals received 5% cellulose. After 6 weeks all gallbladders were inspected for stones; blood and bile were collected for analysis. RESULTS Cholesterol stones were present in 8 of 10 of the control animals, in 6 of 10 of the cellulose group, and 3 of 10 of the PSY animals (P <0.05). Concentrations of cholesterol and chenodeoxycholic acid (CDCA) were significantly lower in the PSY group compared with controls (0.49 versus 0.88 mM and 4.2 versus 9.2 mM, respectively) leading to a significant reduction in the cholesterol saturation index (0.62 versus 1.2). CONCLUSIONS A dietary soluble fiber (PSY) inhibits cholesterol stone formation by reducing the biliary cholesterol saturation index. This protective effect is associated with a selective decrease in biliary cholesterol and CDCA.

Assay of β-glucuronidase in bile following ion-pair extraction of pigments and bile acids

Abstract A method for improving the assay of β-glucuronidase in hepatic and gallbladder bile is described. The method uses ion-pair extraction with N,N,N-triheptyl-l-heptanaminium bromide to remove pigments and bile acids. Conjugated bilirubin, unconjugated bilirubin, and taurine and glycine conjugates of deoxycholic and chenodeoxycholic acids are extracted efficiently from bile by the procedure. The sensitivity of the spectrophotometric assay of β-glucuronidase in bile using phenolphthalein glucuronide is increased significantly.

Action spectrum for oxygen-dependent near-ultraviolet induced corneal damage.

Abstract. An action spectrum for oxygen‐dependent corneal epithelial damage in the rhesus monkey is reported for the near UV wavelength range. The corneal threshold increases monotonically with wavelength throughout the near UV but exhibits a pronounced shoulder in the 340–350 nm region. This behavior is consistent with studies of effects of near UV radiation on bacterial cells. However, the work reported here is unique in that it examines the nature of near UV induced photochemical processes in mammalian cells in situ.

OXYGEN DEPENDENCE OF NEAR-ULTRAVIOLET INDUCED CORNEAL DAMAGE*

Harmful effects of near-ultraviolet ( 3 2 M nm) radiation on cells have been widely reported in recent years (Eisenstark, 1970; Peak, 1970; Pollard, 1974). Such studies have generally dealt with strains of bacteria and have used end points such as percentage of cell lethality (Webb and Lorenz, 1970) or mutagenicity (Kubitschek, 1967; Webb and Malina, 1967) to define the nature and extent of the damage. Reports on the effects of near-UV radiation on ocular tissues are few in number, and primarily involved exposure to low-intensity broad-band light sources over prolonged periods (Zigman et d., 1974; Zigman and Vaughan, 1974). However, two recent papers have discussed corneal and lenticular damage induced by 325 nm radiation from helium-cadmium lasers (MacKeen et af., 1973; Ebbers and Sears, 1975). The work reported here is concerned with ocular hazards of near-UV argon-ion laser radiation in primates. In particular, the most sensitive ocular tissue for the exposure parameters of interest has been found to be the epithelial layer of the cornea. The end point used to define damage is the observation of a macroscopic corneal lesion (analogous to a skin erythema), although in some instances histopathologic examination has been carried out to describe the damage at the microscopic level. The lesions appear as opacities on the surface of the cornea, the shape of the lesion being characteristic of the laser beam dimensions. A recent paper reported the induction of corneal epithelial damage in rhesus monkeys exposed to the near-UV output ( 5 350 nm) of a krypton-ion laser

Measurement of bilirubin partition coefficients in bile salt micelle/aqueous buffer solutions by micellar electrokinetic chromatography.

The partition coefficients for the distribution of bilirubin between aqueous phosphate‐borate buffer and cholic, taurocholic, taurodeoxycholic, and taurochenodeoxycholic micelles have been measured by micellar electrokinetic chromatography at pH 8.5. Determination of the partition coefficients required that the critical micelle concentration and partial specific volumes be determined for each bile salt. Critical micelle concentrations were slightly higher for the trihydroxy bile salts. Partial specific volumes of the bile salt micelles differed very little from each other, and for each bile salt they were constant over the concentration range studied, which was typically from slightly above the critical micelle concentration to 35 mM. Capacity factors were corrected for the effects of applied voltage by extrapolation of the capacity factor to zero applied volts. The free solution mobility of bilirubin, determined in the absence of bile salt, was also corrected for the effects of applied voltage. Plots of extrapolated capacity factor versus phase ratio yield the partition coefficient as the slope of a linear fit to the data. Partition coefficients for bilirubin were significantly higher for dihydroxy bile salts than for trihydroxy bile salts.